Generally, soft-magnetic sheets used in various electronic devices are manufactured by a kneading-rolling method. In this method, a flat soft-magnetic powder, a rubber, and a binder such as chlorinated polyethylene are mixed in a predetermined ratio and are kneaded in a kneader. The obtained kneaded mixture is rolled to a predetermined thickness by, for example, calender rolls and, if necessary, is heated to cross-link the binder, whereby a single-layer soft-magnetic sheet is obtained. Advantageously, with this method, the soft-magnetic powder can be packed at high density and can be oriented in an in-plane direction by rolling, and the thickness of the sheet can be easily adjusted.
However, in the kneading-rolling method, strain is generated in the soft-magnetic powder during kneading, causing deterioration of the magnetic properties of the soft-magnetic powder itself. Therefore, disadvantageously, the soft-magnetic sheet cannot have a large magnetic permeability. In addition, the soft-magnetic sheet changes in a high-temperature environment or a high-temperature high-humidity environment so as to increase in sheet thickness, and the magnetic permeability is disadvantageously reduced.
Accordingly, an application method in which the soft-magnetic powder undergoes less strain is used instead of the kneading-rolling method to manufacture soft-magnetic sheets (Patent Document 1). In this method, a liquid composition for forming a soft-magnetic sheet which is composed of a flat soft-magnetic powder, a rubber, a resin, and a solvent is applied to a release base and is then dried, whereby a soft-magnetic sheet is obtained which exhibits a small change in sheet thickness even in a high temperature environment or in a high-temperature high-humidity environment.
Patent Document 1: Japanese Patent Application Laid-Open No. 2000-243615.